Disposable molds and method of using the same

ABSTRACT

The present invention encompasses, in part, a method and apparatus for lens casting in which two molds, preferably formed of plastic, are interconnected or joined together via a ring to form a mold cavity having substantially the same dimensions of the lens to be formed therein. In one implementation the invention includes a the casting device comprising a plurality of front molds, each front mold formed of a plastic and having a lens-forming surface. The front molds are configured to form a plurality of lenses of different effective diameters. The casting device further includes a rear mold formed of a plastic and having a lens-forming surface; wherein the rear mold is configured to be paired with each of the plurality of front molds to form a plurality of lenses of different effective diameters.

FIELD OF THE INVENTION

The present invention encompasses, in part, a method and apparatus forlens casting in which two molds, preferably formed of plastic, areinterconnected or joined together via a ring to form a mold cavityhaving substantially the same dimensions of the lens to be formedtherein. The invention is further directed to compositions and methodsused in lens casting.

BACKGROUND

The art of casting lenses involves introducing a lens-forming material,such as a monomer or monomer mixture, into a volume and thenpolymerizing the lens-forming material to become a solid. The formedlens can be used for ophthalmic or specialty optics applications.Ophthalmic devices have traditionally been created by first forming acavity out of two separate mold shapes, then filling that cavity with aliquid material that will cure and form a solid shape. The molds used inthis type of process are typically glass or metal, based on their highchemical resistance and low amount of geometric distortion theyexperience over time.

Most commonly, two glass mold pieces and a gasket form the volume thatdefines the dimensions of the lens to be cast. Some prior art gasketsare known as “T-gaskets,” which include a bore having two ends that eachcomplementarily receives a respective glass mold spaced apart apredetermined axial distance from the other mold. Different T-gasketsare required to form varying power lenses because they only allow oneseparation distance between molds. Accordingly, manufacturers mustmaintain T-gaskets for a +2 lens, another for a −3 lens, still anotherfor a −4 lens, etc.

An improvement of this “T-gasket” design is disclosed in U.S. Pat. No.6,068,464 (hereafter “the '464 patent”), in which at least one of thetwo molds is slidably movable along the bore of the gasket. This designthus has a “universal” gasket that can be used to form different powersof lenses, whereas a given prior art T-gasket may be used to form onepower of lens and a different T-gasket is used to form another power.

U.S. Pat. No. 5,551,663 (hereafter “the '663 patent”) described the useof plastic molds in the manufacture of ophthalmic lenses, but no mentionof successfully making lenses is included here. This approachnecessitated the use of a “protective coating” first being applied tothe mold before the mold could be used. This protective coating became apermanent part of the mold, and allowed for the mold to be usedrepeatedly. Evidence of the permanence of the coating is apparent in thedescription of the adhesion test used to assure proper adhesion of thecoating to the mold. The patent describes a “plastic mold having anadherent, abrasion resistant, release enhancing face.” The purpose ofthe coating of the '663 patent is to prevent attack of the mold by thelens material. (By comparison, this current patent application applies acoating to the mold, but with the intent that the coating be onlytemporary, and that it transfer via chemical or physical bonding to thelens material.)

The method of the '663 patent raises significant issues about itsability to consistently produce high-quality molded lenses. Possibleproblems that might occur with the method of the '663 patent include adecay in the optical quality of the mold. Any defect on either side ofthe mold could affect the finished quality of the lens. The decay cantake the form of yellowing, cracking, scratching, and physicaldeformation. These forms of decay can occur with repeated use of anon-rigid material. Any of these types of decay could alter the opticalquality of lenses made. Additionally, plastic materials would bedifficult to clean, since they are not very chemically resistant, notscratch resistant, and not very resistant to the heat used in manytypical processes.

Accordingly, a need exists for durable, low cost plastic molds that canbe used to create lenses of various powers.

SUMMARY OF THE INVENTION

The present invention comprises a method and apparatus for casting alens, and chemical compositions used to perform the same.

In one implementation of the invention, a front mold and a rear moldformed of a plastic are joined together or interconnected via a ring toform a mold cavity having substantially the same dimensions of the lensto be cast. Stated differently, surfaces of the ring and front and rearmolds collectively define a volume known as the mold cavity, which is anegative image of the lens to be formed therein.

More specifically, the front mold has a lens-forming surface and an edgecircumscribing the lens-forming surface. The rear mold similarly has alens-forming surface and an edge circumscribing its lens-formingsurface. The lens-forming surfaces of the front and rear molds are eachof a size to be complementarily received by and within the interiorperiphery of the ring. The molds have backing members, which stop theinsertion of molds when their respective lens-forming surfaces reach apredetermined point within the ring so that the spacing between the twolens-forming surfaces is at a desired separation distance. This desiredseparation corresponds to the thickness of the mold cavity, whichdictates the thickness and power of the lens formed by the castingdevice.

The molds of the present invention may be designed to cast lenses ofdifferent powers, as well as lenses of different effective diametersusing a common rear mold. The effective diameter corresponds to thediameter of the lens that is designed to be a portion of the finishedlens after it has been trimmed to fit a pair of eyeglasses. That is, fora lens with given optical surfaces, the lens thickness can be altered bymanufacturing the front and/or rear molds having their backing member atone of a plurality of distances from the respective lens-formingsurface. Alternatively, the length or height of the ring may be changedto vary the thickness of the mold cavity. Another alternative is toinclude a plurality of protrusions adjacent the edge of one of the lensforming surfaces, in which the height of the protrusions establishes theedge thickness of the mold cavity.

The present invention additionally allows for a disposable plastic moldto be used in the ophthalmic casting process, either with the disclosedapparatus or in other systems known in the art. This disposable mold canbe made out of a variety of amorphous thermoplastics, and can be used tomake a lens with or without a variety of coating scenarios. The lensesformed using this process are impact resistant, can have any refractiveindex, can be (for example) clear (no tint), tinted or photochromic, andcan be used for “dress” or safety purposes.

In one implementation the invention includes a casting device comprisinga plurality of front molds, each front mold formed of a plastic andhaving a lens-forming surface. The front molds are configured to form aplurality of lenses of different effective diameters. The casting devicefurther includes a rear mold formed of a plastic and having alens-forming surface; wherein the rear mold is configured to be pairedwith each of the plurality of front molds to form a plurality of lensesof different effective diameters.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an exemplary embodiment of acasting system used with the present invention.

FIG. 2A is side cross-sectional view of the front mold shown in FIG. 1,which is preferably used to form a minus lens.

FIG. 2B is an alternative design of the front mold shown in FIG. 2A,which is preferably used to form a plus lens.

FIG. 2C is side cross-sectional view of the rear mold shown in FIG. 1.

FIG. 3A is a side cross-sectional view of the components in FIG. 1assembled.

FIG. 3B is an alternative design of the casting system shown in FIG. 3A,in which the front mold of FIG. 2B is included.

FIG. 4A is a lens formed by the casting system shown in FIG. 3A.

FIG. 4B is a lens formed by the casting system shown in FIG. 3B.

FIG. 5 is a perspective view of the casting system of FIG. 1 connectedto a fill bag containing monomer.

FIG. 6A is a side cross-sectional view of an alternative design of ahigh plus front mold shown in FIG. 1.

FIG. 6B is a side cross-sectional view of an alternative design of ahigh minus front mold shown in FIG. 1.

FIG. 6C is a cross-sectional view of a high plus lens formed by thefront mold shown in FIG. 6A.

FIG. 6D is a cross-sectional view of a high minus lens formed by thefront mold shown in FIG. 6B.

FIG. 7A is a cross-sectional view of a first lens.

FIG. 7B is a cross-sectional view of a second lens made using the samerear mold as the lens shown in FIG. 7A.

FIG. 7C is a cross-sectional view of a third lens made using the samerear mold as the lens shown in FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the followingdetailed description, including examples. These examples are intended asillustrative of the invention, and numerous modifications and variationstherein will be apparent to those skilled in the art while stayingwithin the scope of the invention. As used in the specification and inthe claims, “a,” “an,” or “the” can mean one or more, depending upon thecontext in which it is used.

A first embodiment is now described with reference to the figures, inwhich like numbers indicate like parts throughout the figures. Thepresent invention comprises a molding or casting device 10 and anassociated method that may be used to form lenses of various powers andgeometric shapes, such as spectacle lenses. The present inventionadditionally comprises methods for making ophthalmic lenses usingdisposable plastic molds.

In this discussion, first one exemplary embodiment of a casting systemcomprising plastic components is discussed in the context of thecomponents and method of those components. This first discussionprovides context for and is followed by the aspects of the presentinvention that involve casting ophthalmic lenses using plastic molds.This latter discussion is not intended to be limited to the exemplaryembodiment of the casting system disclosed herein.

Lens Casting Devices

Referring now to FIGS. 1–7, the casting device 10 of the presentinvention includes a front mold 20 and a rear mold 40, both of which arepreferably formed of plastic. The casting device 10 also includes a ring50, which may also be referred to as a sleeve or gasket. The ring 50 isalso preferably formed of plastic and has opposed ends 52, an interiorperiphery 54, and an exterior periphery 56. As discussed below, portionsof the front and rear molds 20, 40 are complementarily received by andinto the interior periphery 54 to form a mold cavity 60.

The front mold 20 has a lens-forming surface 22, an edge 28circumscribing the lens-forming surface 22, and a base 30 havingdimensions greater than the interior periphery 54. The edge 28circumscribing the lens-forming surface 22 is sized to becomplementarily received within a portion of the interior periphery 54of the ring 50 and preferably form a substantially liquid-tight sealtherebetween. The edge 28 is slidably received within the interiorperiphery 54 of the ring 50 until the base 30 abuts the end 52 intowhich the edge 28 was inserted.

The rear mold 40 likewise has a lens-forming surface 42, a rim 46circumscribing the lens-forming surface 42, and a flange 48 havingdimensions greater than the interior periphery 54 of the ring 50. Therim 46 is also sized to be complementarily received within the interiorperiphery 54 of the ring 50, which occurs until the end 52 of the ring50 abuts the flange 48. The rim 46 and the interior periphery 54 alsopreferably form a substantially liquid-tight seal therebetween.

As shown in FIGS. 3A and 3B, when the edge 28 of the front mold 20 andthe rim 46 of the rear mold 40 are both received by the respective endsof the ring 50, the lens-forming surfaces 22, 42 of the front and rearmolds 20, 40 and the ring 50 form a mold cavity 60 which has dimensionsof a desired lens formable therein. That is, the mold cavity 60 is areplica image of the lens to be formed and has a volume defined by thering 50, front mold 20, and rear mold 40.

To form a lens once the ring 50 and front and rear molds 20, 40 areproperly joined or positioned together, a resin, such as a monomer orother lens-forming fluid, is added or injected into the mold cavity 60and cured. To that end, the ring 50 defines a feed opening 70 and a ventopening 72 therethrough, which are shown in FIGS. 1 and 5. The ventopening 72 provides fluid communication from the mold cavity 60 tooutside of it (i.e., to ambient).

As best shown in FIGS. 1 and 5, when the front and rear molds 20, 40 aredisposed upright, then the mold cavity 60 is substantially circular inplan view and the vent opening 72 is positioned at approximately the topcenter (the 12:00 o'clock position). The feed opening 70 is preferablyoffset from the vent opening 72, and one contemplated range for thisoffset is by approximately fifteen to ninety degrees (15°–90°). Stillreferring to FIGS. 1 and 5, it will be noted that an extender 74 isjoined to the feed opening 70. The top of the extender in communicationwith the feed opening 70 and is elevationally above the vent opening 72,which ensures that the cavity is full when the monomer reaches the topof the extender 74. It will further be noted that preferably the feedopening 70 is an elongated slot that extends across the width of thering 50. This design ensures that communication exists with the moldcavity 60 through the feed opening 70 regardless of the placement of themolds relative to the ring, which may change when used for casting minuslenses verses plus lenses.

A key dimension of the formed mold cavity 60 is its thickness. For minuslenses used for nearsightedness or myopia shown for example in FIG. 4A,the center thickness is an important parameter, and it must satisfyimpact testing required in the United States. As an example, plasticlenses formed of CR39 (which includes methyl-methacrylate—athermoplastic resin better known by its trademark “Plexiglas”® or“Perspex”®—and diallyl glycol carbonate) must have a center thickness ofat least two millimeters (2 mm). The preferred embodiment of the presentinvention is designed to be able to form both plus and minus lenses thatsatisfy these respective criteria.

First with regard to minus lenses, the center thickness is obtained bythe design of the front and rear molds 20, 40 in conjunction with thewidth or length of the ring 50. Referring now to FIG. 2A and addressingthe front mold 20, its base 30 has a contacting surface 32 that issubstantially planar, and that contacting surface 32 abuts one end 52 ofthe ring 50 when the edge 28 of the front mold 20 is inserted therein todefine a portion of the mold cavity 60. In conjunction, the lens-formingsurface 22 of the front mold 20 is concave and defines a nadir 26 or lowpoint, which tangentially intersects a plane FMP defined by thecontacting surface 32 of the base 30. The nadir 26 of the lens-formingsurface 22 is thus at the same relative height as the contacting surface32 when the front mold 20 is horizontally disposed. As such, the nadir26 is aligned with the end of the ring 50 when the contacting surface 32abuts the end 52 of the ring 50.

As shown in FIG. 2C, the flange 48 of the rear mold 40 has an engagingsurface 49 that is substantially planar to abut the respective end 52 ofthe ring 50 when the mold cavity 60 is formed. The lens-forming surface42 of the rear mold 40 has an apex 44, in which a plane AP tangential tothe apex 44 is substantially parallel to and spaced apart from a planeRMP defined by the engaging surface 49. The separation or distancebetween the plane AP tangential to the apex 44 and the plane RMP definedby the engaging surface 49 is called the back mold apex height AH.

Also, the opposed ends 52 of the ring 50 are spaced apart by a ringheight RH. As one skilled in the art appreciates, the ring height RHestablishes the separation between the engaging surface 49 of the rearmold 40 and the contacting surface 32 of the front mold 20.Correspondingly, the ring height RH is a parameter used to set thecenter thickness of the mold cavity 60, and thus the lens formedtherein. That is, for this embodiment, the center thickness of the moldcavity 60 equals the ring height RH minus the back mold apex height AH,as the nadir 26 of the lens-forming surface 22 of the front mold 20 isaligned with one end of the ring 50. Thus, if the ring height RH isthree millimeters (3 mm) and the back mold apex height AH is twomillimeters (2 mm), then the center thickness—the separation between theapex 44 of the rear mold 40 and the nadir 26 of the front mold 20—is onemillimeter (1 mm).

As shown in FIG. 3A, the assembled casting device 10 shows the relativeposition of the components in establishing the center thickness for themold cavity 60. Specifically, one end 52 of the ring 50 abuts thecontacting surface 32 of the front mold 20 and the opposed end 52 abutsthe engaging surface 49 of the rear mold 40. The nadir 26 of the frontlens-forming surface 22 is spaced apart a desired distance—the centerthickness—from the apex 44 of the rear lens-forming surface 42 when themolds 20, 40 are coupled together. Stated differently, the plane APtangential to the apex 44 is spaced apart from the plane FMP defined bythe contacting surface 32 and tangentially intersects the nadir 26 at adistance substantially equivalent to the desired center thickness of themold cavity 60. Thus, the apex 44 and the nadir 26 of the respectivelens-forming surfaces 22, 42 in the mold cavity 60 are spaced apart atthe desired center thickness for the lens to be formed.

As one skilled in the art appreciates, changing the dimensions of thecomponents correspondingly alters the center thickness of the moldcavity 60. Any of the components can be modified. Although viable,currently the least desirable option is to change the position of thenadir 26 relative to contacting surface 32 of the front mold 20. A moredesirable option is using rings 50 each having a different ring heightRH to change the center thickness. The presently preferred design,however, is to vary the back mold apex height AH among different moldsto change the center thickness of the mold cavity 60. Thus, in thislatter design, the front mold 20 uses the same design shown in theillustrated embodiment and a “universal” or “one-size” ring that has thesame dimensions regardless of the strength of the lens to be made; onlythe rear mold 40 is changed in this latter design and, in particular,the back mold apex height AH is altered among different rear molds 40 tovary the center thickness of the mold cavity 60.

Still another contemplated embodiment to change the center thickness fora selected ring 50, front and rear mold 20, 40 is to include a circularspacer (not shown) between the engaging surface 49 of the rear mold 40and respective end of the ring 50. The circular spacer has diameter thesame as the ring 50 and a fixed width or height, thereby increasing thecenter thickness of the mold cavity 60 by that width of the circularspacer. For example, a circular spacer having a width of one millimeter(1 mm) disposed between the end of the ring 50 and the engaging surface49 would correspondingly result in the center thickness of the moldcavity 60—and lens to be formed therein—increasing by one millimeter (1mm). Circular spacers, accordingly, may reduce the number of componentsthat need to be manufactured to enable an operator to cast all desireddimensions and strength of lenses.

Referring now to FIGS. 2B and 3B, the illustrated front mold 20 includesa plurality of protrusions 34 located adjacent the edge and spaced apartfrom each other. The protrusions 34 have a height corresponding to adesired edge thickness for the mold cavity 60. For example, if theprotrusions 34 have a height of one millimeter (1 mm), then the edgethickness of mold cavity 60 will be at least one millimeter because theprotrusions 34 prevent the edges of the front and rear lens-formingsurfaces 22, 42 from being closer together than the height of theprotrusions 34. The protrusions 34 may be any desired height, includingfor example 0.75, 1.0, 1.25 millimeters and the like. A person skilledin the art can determine the number of protrusions 34 to use; thecurrently contemplated embodiment uses thirty-two equally spacedprotrusions 34 circumscribing the perimeter of the lens-forming surface22 of the front mold 20. Fewer protrusions are shown in the drawings forsimplicity. It will be appreciated that benefits of this design includethe same rear molds 40 and rings 50 that are used to form the minuslenses also being used to form the plus lenses.

The present invention additionally contemplates other methods of formingplus lenses. For example, the ring height RH may be varied to obtain thecorrect separation between the lens-forming surfaces 22, 42 of the frontand rear molds 20, 40, including the edge thickness. Also, thelens-forming surfaces 42 of the rear molds 40 may include theprotrusions 34 instead of the front molds, but this option is lessdesirable given the greater variations in rear mold designs andassociated higher cost for a “library” of molds to manufacture all lensvariations.

Another relevant parameter in forming a desired lens is the geometricconfiguration or relationship of its two optical surfaces. When the twolens-forming surfaces 22, 42 are both spherical, the molds 20, 40 do notrequire any special rotational alignment relative to each other. This isbecause the respective surfaces have a constant radius along theirdifferent axes resulting in the surfaces being symmetric relative toeach other.

For other lenses, however, the present invention includes a means fororienting the front and rear molds 20, 40 at a predetermined rotationalposition with respect to each other. In the illustrated embodiment, thefront and rear molds 20, 40 are rotatably movable relative to each otherso that the two molds may be positioned at one of a plurality ofselected relative rotational orientations. This orienting means thusallows the operator to alter the dimensions or shape of the mold cavity60 to desired values when either or both of the lens-forming surfaces22, 42 of the front and rear molds 20, 40 have asymmetric curvature.Examples of asymmetrical lenses that operators may typically castinclude the front surface of a lens being spherical with an add power—orless frequently being a piano surface—and, in conjunction orindependently, the back surface being cylindrical or toric. A discussionof the features and types of such asymmetrical surfaces may be found inU.S. Pat. No. 6,103,148.

Referring back to FIG. 1, the present invention also comprises analigning means to allow the operator to appreciate the relative rotationof the two molds 20, 40 and position them accordingly. The aligningmeans shown in the illustrated embodiment comprises axis marks 90 on theexterior periphery 56 of the ring 50 and an axis-positioning indicator92 on the front mold 20 or rear mold 40 or both. The axis marks 90extend from 0° to 180° and the asymmetrical lens-forming surface 22 or42 is to be positioned in registry with them. If injection molding orsimilar technique forms the components, the aligning means arepreferably etched or formed into the respective dies. Thus, the positionindicator 92 and marks 90 are also integrally formed into thecomponents. One skilled in the art will also appreciate that aligningmeans may alternatively comprise the axis marks being located on one orboth of the front and rear molds 20, 40 and an axis-positioningindicator on the ring 50. Other methods of visually indicating therotational position of the molds relative to each other may also beused.

In preparing to cast the lens, the operator locates the positionindicator 92 at a desired orientation relative to the axis marks 90 onthe ring 50 either before the front and rear molds 20, 40 are joined tothe ring 50 or afterwards (e.g., by being aligned before they are putinto the ring, then pushed into the ring.) the molds relative to eachother once they are coupled to the ring 50). The operator, thus, is ableto position the two molds at a desired rotational location easily usingthe aligning means.

When the operator joins the ring 50 and the two molds 20, 40 togetherafter selecting them, it is preferred that a connecting means exists sothat the components do not inadvertently separate during the lenscasting process. Such a connecting means can take numerous forms knownin the art, including the interior periphery 54 of the ring 50 and theedge 28/rim 46 having a tight frictional fit. Other connecting means arealso contemplated (not shown), including designs in which the two molds20, 40 snap into place within the ring 50 or in which an external clipor containing device is used to hold the components together.

In still another contemplated embodiment, the front and rear molds 20,40 are formed as a single unit so they are integrally joined to eachother. This may occur during the forming process (i.e., during injectionmolding) so that the operator receives a preformed molding structure inwhich the front and rear molds 20, 40 are stationarily positionedrelative to each other. This unitary design, however, has lessflexibility than interchanging the ring 50 and the front and rear molds20, 40.

As noted above, once the front and rear molds 20, 40 are stationarilypositioned together, a resin, such as a monomer or other lens-formingfluid, is added or injected into the mold cavity 60 via the feed andvent openings 70, 72 through the ring 50, and then cured. Referring nowto FIG. 5, a fill bag 80 or the like containing a fluid such as monomermay be interconnected to the feed opening 70 or its extender 74. Morespecifically, the fill bag 80 has an interior and an injection port 82detachably connectable to the feed opening 70. When the injection port82 is linked to the feed opening 70, the monomer located within theinterior of the fill bag 80 may flow through the port into the moldcavity 60.

The injection port 82 and the feed opening 70 are preferably designed tocomplementarily engage each other. That is, the tip 84 of the injectionport 82 is of a size to be complementarily received within the feedopening 70 or its extender 74 to form a fluid-tight seal therebetween.

One consideration that a person skilled in the art takes into account incasting lenses is the flow characteristics of the monomer traversingfrom the fill bag 80 into the mold cavity 60. A primary concern is toavoid the introduction of air bubbles and ensure that any such bubblesescape from of the mold cavity 60 before the curing begins; otherwise,the formed lens may be unacceptable if an air bubble discontinuityexists in the final product. In addressing this issue, the size of thefeed opening 70 should be of a dimension and positioned to promotelaminar flow when filling the mold cavity 60. The fill opening 70 ispreferably oriented to direct the monomer along the side of the moldcavity 60 during the initial filling. As noted above, the vent opening72 is also preferably located at the top of the mold cavity 60 (i.e., atthe 12:00 o'clock position) to vent air within the cavity 60 whendisplaced by the injected or incoming monomer. The vent opening 72 beinglocated at the top also allows any bubbles to escape before the curingprocess begins.

Another consideration regarding injecting monomer involves positioningthe mold cavity 60 so that the add power (not shown) is oriented to haveits flat top portion substantially upright or vertical during fillingthe mold cavity 60. This orientation assists in preventing air bubbleswithin the monomer from being trapped by this discontinuity in thelens-forming surface 22 of the front mold 20. Bubbles are more likely toremain in the mold cavity 60 if, for example, the flat top ishorizontally oriented.

Referring again to FIG. 5, the fill bag 80 is at least partiallyconstructed of a deformable surface on which the operator directs acompressive force so that one wall of the bag 80 moves inwardly towardthe opposed wall. When that compressive force is applied, the fluidmonomer located within the interior is forced toward and out of theinjection port 82 to enter the mold cavity 60 via the feed opening 70.In constructing a system necessitating minimal capital investment, theillustrated embodiment is inexpensively designed and relies on theoperator hand squeezing the bag 80 to fill the mold cavity 60.

Other means of injecting monomer into the mold cavity 60 arecontemplated. Examples of such systems using a deformable bag to fillthe mold cavity 60—particularly for more complex casting designs—isdisclosed in U.S. patent application Ser. No. 10/095,130, filed on Mar.11, 2002 and entitled “Method and Apparatus for Dispensing a Fluid”.Monomer fill systems similar to the design disclosed in U.S. Pat. No.6,103,148 is another option.

Once monomer fills the mold cavity 60, the bag 80 is separated from themold and then the monomer is cured (as discussed in more detail below).

Mold Materials

Materials suitable for forming the molds of the invention include avariety of thermoplastic or substantially thermoplastic materials thatcan be injection molded. The materials are preferably opticallytransparent. Suitable amorphous thermoplastic materials include, but arenot limited to, polycarbonate, acrylics, polystyrene, CAB (celluloseacetate butyrate), polyesters, and combinations thereof. In general itis also desirable that the thermoplastic material be selected such thatit will not be attacked by coating and/or monomer material used to formthe lens. In general higher molecular weight analogs of thermoplasticsare desirable because they are typically more resistant to coatings andmonomers used to form the lenses.

Amorphous thermoplastics can provide the advantage that, unlikecrystalline thermoplastics, they tend to maintain an optical-qualitysurface for long periods of time, and so have a long shelf life withproper storage. In contrast, crystalline thermoplastics, such aspolypropylene undergo dimensional changes after they are injectionmolded. These dimensional changes occur due to the polymer's attempt toarrange itself in a more crystalline structure. The result of thisrearrangement is that the plastic part can have an uneven, non-opticalsurface. In contrast, amorphous thermoplastics will typically retain theshape they took on during the injection molding process. Not allthermoplastics are either 100% crystalline or 100% amorphous, so thescope of this disclosure ranges from “substantially amorphous” tototally amorphous materials, meaning thermoplastics that contain mostlyamorphous materials.

Pre-Release Control

As one skilled in the art will appreciate, the lens formed for a highpower lens (either “high plus” or “high minus”) can have substantialdifferences in thickness between the middle of the lens and the edge ofthe lens. The lens forming material will have some shrinkage during thecure process, and large differences in thickness will lead to largedifferences in shrinkage. When the outer periphery of the lens shrinkssubstantially more than the inner portion of the lens (such as with ahigh minus lens), or when the inner portion of the lens shrinks morethan the outer periphery of the lens (such as with a high plus), theportion of the lens with higher shrinkage will actually pull away fromone or more of the mold surfaces, resulting in a condition known tothose in the optical industry as “pre-release.”

To reduce pre-release in high power lenses using glass molds, a new setof front and back molds have to be made in smaller diameters.Accordingly, new gasket sets must also be made for the new molds.Specifically, in the present invention, pre-release in high power lensesis controlled by changing only the front mold geometries withoutchanging the back mold or the ring used to assemble the front and backmolds together. In fact, the rings and back molds are the same ones usedfor the rest of the lens powers, thus no additional small diameter backmold inventory is required to accommodate high power lens manufacture.

FIG. 6A shows a cross-sectional view of a front mold 100 for a high pluslens. Relative to a standard front mold 20 for a plus lens disclosed inFIG. 2B, the geometry of the lens forming surface has been changed froma uniform spherical shape to a mold that comprises a center region 102and an outer region 104. Center region 102 comprises a spherical surfacewith a radius of curvature R1. Center region 102 extends from thecenterline of mold 100 to a distance X1 away from the centerline of mold100, and outer region 104 extends from distance X1 away from thecenterline to the outer periphery of the mold 100. Outer region 104comprises a surface that has a radius of curvature R2 that issubstantially greater than R1, which may comprise a surface that is flat(infinite radius of curvature).

When coupled with a standard-shaped rear mold 40, a finished lens 106made with front mold 100 would have less of a thickness differencebetween the center and edge of the mold, thereby reducing or eliminatingthe pre-release of the lens from the mold. Specifically, referring toFIG. 6C, finished lens 106 comprises a first surface 108 formed bycontact with regions 102 and 104 of front mold 100, and a second surface109 formed by contact with standard rear mold 40. The thickness of thecross section of finished lens 106 is a function of the different radiiof curvature and loci of the radii of curvature of the surfaces of molds100, 40. Generally, lens 106 will comprise a maximum thickness at thecenterline of the lens, shown in FIG. 6 as distance Y1. On account ofthe differences in radii of curvature and loci of the radii ofcurvature, the thickness of the lens will be generally decreasing atincreasing distances away from the centerline of the lens 106. Thethickness of the lens 106 will decrease up to distance X1 from thecenterline of the lens. At distances greater than X1, on account of theshape of region 104 of mold 100, the thickness of the lens will increasewith increasing distance from the centerline. The minimum thickness ofthe lens, denoted as distance Y2 in FIG. 6C, is formed at distance X1from the centerline of the lens. If region 104 were not present, theminimum thickness would typically exist at the outer periphery of thelens, i.e. the maximum distance away from the centerline of the lens,and would typically be smaller than distance Y2. Accordingly, thedifference between the minimum thickness and the maximum thickness isreduced with mold 100, minimizing the potential for pre-release.

Referring now to FIG. 6B, a cross-sectional view of a front mold 110 fora high minus lens is shown. Relative to a standard front mold 20 for aminus lens disclosed in FIG. 2A, the geometry of the lens formingsurface has been changed from a uniform spherical shape to a mold thatcomprises a center region 112 and an outer region 114. Center region 112comprises a spherical surface with a radius of curvature R3 and outerregion 114 comprises a spherical surface with a radius of curvature R4.Radius R3 is substantially larger than radius R4. Center region 112extends from the centerline of mold 110 to a distance where a tangent toradius R3 aligns with a tangent to radius R4, denoted on FIG. 6B asdistance X2.

When coupled with a standard-shaped rear mold 40, a finished lens 116made with front mold 110 would have less of a thickness differencebetween the center and edge of the mold, thereby reducing or eliminatingthe pre-release of the lens from the mold. Specifically, referring toFIG. 6D, finished lens 116 comprises a first surface 118 formed bycontact with regions 112 and 114 of front mold 110, and a second surface119 formed by contact with standard rear mold 40. The thickness of thecross section of finished lens 116 is a function of the different radiiof curvature and loci of the radii of curvature of the surfaces of molds110, 40. Generally, lens 116 will comprise a minimum thickness at thecenterline of the lens, shown in FIG. 6D as distance Y3. On account ofthe differences in radii of curvature and loci of the radii ofcurvature, the thickness of the lens will be generally increasing atincreasing distances away from the centerline of the lens 116. Thethickness of the lens 116 will increase up to distance X2 from thecenterline of the lens, where the thickness of the lens is a maximumvalue of Y4. At distances greater than X2, on account of the shape ofregion 114 of mold 110, the thickness of the lens will decrease withincreasing distance from the centerline. If region 114 were not present,the maximum thickness of lens 116 would typically exist at the outerperiphery of the lens, i.e. the maximum distance away from thecenterline of the lens, and would typically be greater than distance Y4.Accordingly, the difference between the minimum thickness and themaximum thickness is reduced with mold 110, minimizing the potential forpre-release.

Certain aspects of the invention are directed to casting devicescomprising a ring having an interior periphery and a plurality of frontmolds, each front mold formed of a plastic and having a lens-formingsurface. The front molds provide an edge circumscribing the lens-formingsurface that is sized to be complementarily received within a portion ofthe interior periphery of the ring, and a base having dimensions greaterthan the interior periphery. The casting devices further include a rearmold formed of a plastic and having a lens-forming surface, the rearmold configured to be paired with each of the plurality of front molds.The edge of each of the front molds and the rim of the rear mold areconfigured to be received by the ring, the lens-forming surfaces of thefront and rear molds and the ring form a mold cavity which hasdimensions of a desired lens formable therein. The plurality of frontmolds are configured to form lenses of different effective diameters.

The molds of the present invention may be designed to cast lenses ofdifferent powers, as well as lenses of different effective diametersusing a common rear mold. The effective diameter corresponds to thediameter of the lens that is designed to be a portion of the finishedlens after it has been trimmed to fit a pair of eyeglasses. Referringnow to FIGS. 7A to 7C, the effective diameters of three lenses madeusing three different front molds and a common rear mold are depicted.In FIG. 7A, the lens 206 has an effective diameter A–A′; in FIG. 7B thelens 216 has an effective diameter of B–B′; while in FIG. 7C the lens226 has an effective diameter of C–C′. It will be observed that lenses206, 216, and 226 can all be common rear mold. Thus, each of front molds20, 100, and 110 can be used with the same rear mold 220 to make lensesof three different effective diameters.

Mold Coatings

In certain embodiments of the invention a coating is applied to theinterior of the mold prior to forming the lens. In some embodiments thecoating is applied to interior portions of the mold by dip coating, spincoating, spray coating, flow coating, electrostatic spray, roll coating,modified roll coating, print coating, or other coating method. Thecoating may then optionally also be subjected to a “precure” topartially cure the coating so that it will stay in place and not moveduring subsequent steps in the process.

The molds can be coated with any of a variety of coating formulations,provided that the coating does not chemically attack the mold. Thecoating formula can include, for example, acrylate functional materialscapable of crosslinking, sol-gels, nanoparticle-based coatings,initiators or catalysts capable of initiating the reaction of acrylates,flow or leveling agents, defoamers, stabilizers, UV absorbers,antioxidants, dyes, and possibly solvents. Some solvents can be used inthe coating formulation, as long as such formulations do notsubstantially attack the mold before the formulation has cured. Solventsthat could be used would include alcohols, glycols ethers, etc. Solventsthat would be less acceptable for use would include lower molecularweight ketones such as acetone, methyl ethyl ketone, methyl isobutylketone (MIBK), cyclohexanone; acetates; aromatic solvents such asbenzene, xylenes; low MW hydrocarbons such as hexane, etc.

Suitable coatings include those that provide a hardcoat for improvedscratch-resistance, a tintable coat for the purpose of making sunglassesor other “fashion” tints, a UV coat to prevent certain wavelengths of UVlight to pass through the lens, an AR (“anti-reflective”) coat toprevent glare, or any other type of ophthalmic coating. The coatingshould be selected so that it does not attack the mold material. Suchcoatings remain on the mold temporarily and are transferred to thefinished lens during the lens curing step. Thus, the coating is appliedto the mold with the intent that it becomes an integral part of thefinished lens.

In general it is important that the coating not attack the interior ofthe mold and be readily releasable from the mold. Accordingly, coatingformulations should not have enough solvating power to attack the mold.As one skilled in the art would appreciate, the coatings could be basedon UV-curable acrylic, sol-gel, or other composition types. The coatingpreferentially has a more complete cure at the mold/coating interfacethan at the coating/air interface.

In an acrylic coating, the major constituents of the protective coatinginclude multifunctional acrylates or methacrylates, includingtri-,tetra-, penta-, and hexafunctional materials capable of providinghigh levels of cross-linking. The molecular weight of these constituentsmust be high enough to prevent attack on the mold. The protectivecoating could contain a small amount of a low-viscosity diluent with atleast two ethylenic groups to adjust for coating viscosity, but themajority of the formulation will contain higher molecular weight, higherviscosity materials. Examples of materials commonly used in coatings arein the attached table and illustrate the importance of the use ofappropriate materials with plastic molds.

Lens Forming Formulations

The molds of the present invention are suitable for use with a varietyof resin compositions to form finished optical lenses. In general, moldsmade in accordance with the invention are well suited to the use ofradiation initiated curing processes, such as by exposure to ultravioletor visible light, but can also include thermally cured materials if thethermal cure temperature is below the glass transition temperature T_(g)of the mold.

Suitable lens forming compositions include materials having low curetemperatures, which cure quickly, including acrylates and methacrylates.In some implementations epoxies can be used.

It is generally desirable to have the lens forming formulation be inertor substantially inert to the mold itself. However, in certaincircumstances the lens material is not inert to the mold material, inwhich case an intermediate, transferable, coating material can be usedto prevent degradation of the mold. Typically the coating is appliedfirst to the interior of the mold, cured or partially cured, and thenthe primary lens forming formulation is added.

Any of a variety of photocleavable or thermal initiators can be used.The level of photo initiator or thermal initiator used is typically low(less than 5%) and would not have a significant impact on the chemicalaggressiveness of the lens formulation on the mold. In general, lowertemperature curing of the lens is preferred, accomplished with UV orvisible light photo initiators, low initiation temperature thermalinitiators or a combination of both. A variety of light sources can beused, including those with output in the UV-A, UV-B and visible ranges,or combinations thereof.

Depending on the choice of thermoplastic materials used, there will becertain chemistries and/or process parameters that will allow the moldto be used satisfactorily. Based on the simple chemical notion that“like dissolves like,” each different type of thermoplastic material canbe used without issue with certain ingredients typical of a coatingformulation and/or lens formulation. In order to determine if a rawmaterial (or group of raw materials in a formulation) will be chemicallycompatible with mold material, any number of tests can be employed:

One screening test for chemical compatibility involves a representativesample of the thermoplastic material to be placed in close contact withthe chemical to be tested. This “close contact” can involve soaking thethermoplastic in the test solution, or the test solution can be allowedto sit on top of the thermoplastic material. The time and temperatureduring which the two materials are in contact are controlled variablesin the test. After the test period is over, all excess test solution isremoved from the thermoplastic material by simple wiping, and thethermoplastic is evaluated for any damage by measuring any change inphysical appearance, any change in percent transmittance, any change inrefractive index, any change in tensile strength, any change inflexibility, any change in weight or size, any change in surfacesmoothness, or any change in optical properties.

In certain embodiments of the invention, the formulation used to formthe lenses and the material used to form the mold is selected based uponsolubility properties of the mold material and the lens formingformulation. In general it is desirable to have low solubility of themold material in the lens forming formulation. Although it is difficultto determine solubility of a solid material in a resin, the durablity ofthe mold can be used as an indication of solubility. Applicants havefound that the lens forming formulation should be selected such that theresin does not significantly degrade optical properties of the moldsurface upon exposure to the resin.

Any significant change in any of the above properties of thethermoplastic constitutes damage to the material, and the thermoplasticmaterial cannot be used with that test solution. However, it is stillquite possible that although a certain ingredient is known to attack aparticular thermoplastic material, that ingredient can still be used insmall amounts in solution, provided that the other components arecompatible with the thermoplastic. Numerous examples of such scenariosare provided for in this patent.

Methods for Casting and Curing Lenses

The present invention is also directed to methods for casting lenses.For an initial step, the method of the present invention involvesproviding the ring 50 and front and rear molds 20, 40. Although it iscontemplated that the components be pre-connected together as a unit andprovided to the operator, it is preferred that the ring 50 and front andrear molds 20, 40 are preferably combined or coupled together by theoperator at the lens manufacturing location to form the mold cavity 60.When the operator receives the prescription of a spectacle lens, he orshe selects the front and rear molds 20, 40 that, together, form a moldcavity 60 having the dimensions of the desired lens. In the illustratedembodiment, the ring is a “one-size” or “universal” ring and used tomanufacture all lenses, whether plus or minus and regardless of power.

To that end, the ring 50 and front and rear molds 20, 40 are movablebetween a stored position and a molding position. In the storedposition, the components are separated from each other, in which moldshaving the same characteristics are stored together in designated areasor bins. In the molding position, the protrusion 46 of the rear mold 40receives the edge 28 of the front mold 20 to form the mold cavity 60after the operator retrieves the correct molds from the designatedstorage areas.

It is contemplated using computer or other system (not shown) to assistthe operator in selecting the correct molds 20, 40 when preparing tocast a lens. As one example, the present invention contemplates that theoperator enters the parameters of the lens to be formed (e.g., theprescription including add power) into a computer or the like.Algorithms in an associated computer program determine the appropriatefront and rear molds 20, 40 to be used to form the desired lens and thenprovide an output indicating this information. As one optionalvariation, such a system may additionally illuminate a light or provideanother indicator at the storage stations above the specific locationwhere the appropriate molds 20, 40 are stored. The indicators assist theoperator in locating the appropriate molds to reduce the chance of theoperator inadvertently picking an incorrect mold to make the lens. Yetanother option is to use a bar code or other tracking system (not shown)on the outer surfaces of the molds 20, 40 that the system scans toverify that the two proper molds are being used.

After the operator locates the front and rear molds 20, 40, obtains aring 50, and is ready to join the components together, the output of theoptional computer system may further assist the operator by indicatingadditional positioning and aligning information. As discussed above, inthe illustrated embodiment the front and rear molds 20 are rotatablymovable relative to each other so that the two molds 20, 40 are at oneof a plurality of selected rotational orientations relative to eachother. The computer may provide an output indicating the orientation ofthe two molds 20, 40 relative to each other when the lens-formingsurfaces 22, 42 of the respective molds have asymmetric curvature. Forthe illustrated embodiment, the computer preferably indicates theappropriate location of the axis-positioning indicator 92 to be alignedon the axis marks 90.

As to the positioning of the molds 20, 40 to obtain the correct centeror edge thickness for the mold cavity 60, this parameter is preferablyconsidered in selecting the ring 50 and molds 20, 40, as discussedabove. The designated components are preferably manufactured so thatwhen the operator combines or assembles the components together, themold cavity 60 has the correct thickness without any additional actions.

However, one skilled in the art will appreciate that other means besidesa computer system may be used to determine the correct mold to use withthe present invention. Notably the present invention utilizing thecomputer system allows an operator with minimal training andunderstanding of the principles of lens casting to manufacturesuccessfully lenses when a customer provides a prescription.

After the front and rear molds 20, 40 are joined with the ring 50 toform the mold cavity 60 of the desired dimensions, the operator connectsthe bag 80 or other source of monomer to the feed opening 70. Theoperator then injects the monomer into the mold cavity 60.

During filling, the monomer enters via the feed opening 70 while thevent opening 72 allows displaced air to exit the mold cavity 60 toambient. The filling method used with the present invention minimizesthe quantity of monomer wasted and decreases the chances of air bubblesbeing formed within the lens. If used, the bag 80 may contain a quantityof monomer that is sufficient to form only a single lens or,alternatively, for multiple castings.

Because monomer is a viscous fluid, it will inherently fill the moldcavity 60 at a controlled rate. By design, the fill rate may be furthercontrolled by reducing the cross-sectional area of the feed opening 70and/or the tip 84 of the bag 80. Since the front and rear molds 20, 40are formed of plastic, they can be clear or transparent so that theoperator may visually observe the monomer entering and filling the moldcavity 60. When the cavity 60 is filled with monomer so that the monomerreaches the vent opening 72 (and thus the top of the extender of thefeed opening 70), the monomer source is removed from the ring 50. Ifnecessary, the feed opening 70 is plugged, which may simply involve spotcuring the monomer at that location to plug it or using a covering thatsnaps into the feed opening 70. The vent opening 72, however, preferablyremains in communication with ambient during curing.

The monomer within the mold cavity 60 is then cured to form the lensafter ensuring that no bubbles are present. The lens material, dependingon the formulation, can be cured with a variety of methods, includinglight, heat, or combinations thereof. If a free-radical mechanism isemployed, then the lens can be cured via either UV light, visible light,or heat, depending on the initiator. It is also possible to cure thelens with a combination of these curing techniques. These curing methodscan be used either simultaneously or sequentially.

Both curing techniques can be used with a variable rate of cure (i.e.,ramp-up, progressive cure.) After the cure cycle is complete (typicallyfrom two to ten minutes) the lens is removed from the molds simply beremoving the gasket, and lifting the molds away from the lens.

Methods of Making Lenses Using Plastic Molds

The present invention is also directed to methods of casting lensesusing plastic molds, which may be used with the exemplary embodimentdiscussed immediately above or another design (i.e., a T-gasket designthat uses plastic molds instead of glass molds).

When selecting the specific type of material to form the molds, oneskilled in the art will appreciate that to be useful in curing monomer,the selected plastic must transmit the curing radiation without melting,deforming, or stretching—at least until after the monomer issubstantially cured or polymerized. Although thermal radiation iscontemplated as a curing source and falls within the scope of thepresent invention, one skilled in the art will appreciate that thepresent invention may be better suited for photo curing.

For photo curing of liquid resins, the desirable plastics includeacrylic and methacrylic materials, an example of which ispolymethylmethacrylate (PMMA). Some embodiments of available lighttransmissive PMMA are the OP1 and OP4 products by Cyro Industries, UV-Tand V8-25 by Rohm & Haas, and CP-75 from ICI. Other exemplary types ofradiation transmissive plastics that may be used with the presentinvention include amorphous polyesters, amorphous polyamides, amorphouspolyurethanes, amorphous polyolefins, amorphous polycarbonates,amorphous polyimides and co-polymers thereof. One skilled in the artwill appreciate that these listed plastics are illustrative and thepresent invention is not limited to these examples.

Another factor that one skilled in the art considers in selecting theplastics to use is that they do not adversely interface or react withthe material to be cured. If, for example, it is desired to usepolymethylmethacrylate to form the molds based on its cost or physicalproperties, then compatible monomers include long chain or highmolecular weight monomers or prepolymers that do not attack the moldshould be used. Alternatively, the monomer desired to be used may be theprimary consideration and the plastic forming the molds is chosen basedon it being chemically resistant and non-reactive to that selectedmonomer.

Using plastic to form the molds provides potential benefits over castingsystems currently used in the industry. One consideration is that theplastics may be injection molded. There is extensive use and experiencein the industry of injection molding polymethylmethacrylate and acrylicsusing ceramic or metal molds. To that end, the molds may be formed, forexample, by fabricating metal dies into which polymethylmethacrylate orother plastic is injection molded in an assembly process having a highthroughput. Each of the molds, accordingly, will be formed to the samehigh tolerances to which the die is formed. Glass molds, in contrast,cannot be fabricated to such exacting standards, so the presentinvention can cast an ophthalmic lens that is formed to more rigorouscriteria. One skilled in the art will further appreciate that theplastic components may be formed using other suitable high throughputmethods used in the art for fabricating plastics, in contrast to glassmolds that cannot feasibly be mass-produced to the requisite tolerances.

Another consideration with using plastic components is the economiccomparison with conventional prior art systems using two glass molds anda gasket. Although glass molds may be repeatedly used up to one hundredtimes or more, expenses accumulate that are associated with eachcasting, such as washing and drying that must ensure that thelens-forming surface is not contaminated. In fact, cleaning processesfor glass molds are typically laborious, time-consuming and inefficient,involving manual scraping and soaking in noxious solvents. Furthermore,the glass molds must be inspected after each use and cleaned to insuresuitability for another lens-making cycle. Plus, many times the glassmolds are inadvertently chipped and/or broken before their potentialuseful life is reached. An associated problem is the occurrence of lensyield loss resulting from unwitting reuse of damaged lens molds, inwhich the operator sometimes does not discover that a glass mold isdamaged until after a casting process has been completed.

Yet another aspect of the present invention involves coating thelens-forming surfaces of the molds with an abrasion-resistantcomposition that is transferred to the lens when cured. Morespecifically, the lens-forming surfaces are preferably covered with acomposition that transfers in situ to the optical surfaces of the castlens as a protective coating on the final product. Without such a hardcoating on the lens that prevents or resists abrasion, scratching, andmarring, the optical quality of the cast spectacle lenses may moreeasily degrade from haze and poor image quality.

Another example of such an abrasion-resistant coating is disclosed inU.S. Pat. No. 5,049,321. This patent discloses that the coatingcomposition consists substantially of reactants having at leasttriacrylate functionality, a photoinitiator, and a polymerizationinhibitor reactive with oxygen. After applying such a coatingcomposition in the form of an ultraviolet curable liquid to the mold,the coating is subjected to ultraviolet radiation in anoxygen-containing environment such that the coating composition is curedto a semi-cured state. Then, when casting and curing the ophthalmiclens, the monomer is permitted to harden and react with acrylate groupsat the coating/lens interface so that the coated lens is removed fromthe mold with the abrasion-resistant coating adhering thereto as anintegral part of the surface of the optical surfaces of the lens. Othersimilar techniques of forming an abrasion-resistant coating on a castlens are disclosed in U.S. Pat. Nos. 4,338,269 and 4,758,448.

One skilled in the art will appreciate that, although not necessary,using such an abrasion-resistant coating on the lens-forming surfacesproduces a final product that consumers may prefer and that also allowsthe operator to separate more easily the molds from the lens casttherebetween. To that end, the abrasion-resistant coating may be appliedto the lens-forming surfaces of the molds using a process the same as orsimilar to that disclosed in U.S. patent application Ser. No.10/075,637, filed on Feb. 12, 2002 and entitled “Methods of Applying aCoating to an Optical Surface”. Alternative treatment methods of themolds known in the art include spraying, dipping, brushing, flowcoating, spin coating, and the like.

The preferred method involves curing using photo curing, although othercuring methods are contemplated in conjunction with or alternatively tolight. One primary advantage of photo curing, such as UV radiation, isthat the plastic molds do not reach a temperature at which they maymelt, deform, or stretch, which is more likely to occur with thermalradiation curing. UV curing methodologies are taught, for example, inU.S. Pat. Nos. 4,919,850; 5,524,419; 5,804,107; 5,981,618; 6,103,148;and 6,241,505.

After the monomer is cured to harden, then the operator removes thecured lens from within the mold cavity. It is contemplated that theplastic components of the present invention will have a one-use life.That is, the molds can be disposable so that there are no problems ifthe molds are chipped or broken during the removal of the lens from themold cavity. In fact, breaking the molds may assist in separating thecured lens from the mold cavity 60, as the molds are more brittle thanthe cured lens so the lens does not also break. One skilled in the artwill also appreciate that treating the lens-forming surfaces withabrasion-resistant coatings, such as the compositions disclosed in U.S.patent application Ser. No. 10/712,714 and U.S. Pat. No. 5,049,321, willassist in separating the lens from the mold as well as providing thelens with a protective scratch-resistant barrier. One skilled in the artwill further appreciate that the plastic molds of the present inventioncan be used for more than one casting before their useful life ends.

EXAMPLES

The invention will now be further understood by reference to thefollowing examples. As used in these examples, SR 340 is themonofunctional monomer 2-phenoxyethylmethacrylate; SR 506 is isobornylacrylate; SR 150 is ethoxylated bisphenol A dimethacrylate; Ebecryl1039, which is a urethane monoacrylate; Ebecryl 810, which is apolyester tetraacrylate; CN 131 is a low viscosity aromatic monoacrylateoligomer; and SR 203 is a tetrahydrofurfuryl methacrylate monofuntionalcyclic monomer. All numbers below are in parts. The lenses were curedbetween two acrylic molds. The cure time was 5 minutes (except for the100% SR 203 formulation, which was cured for 30 minutes). Theformulations were photocured.

Examples 1 to 3 Lens Formation Interaction

These examples show how diluting an aggressive formulation componentwith a non-aggressive component can modify the mold-formulationinteraction.

Example 1

The molds for Example 1 were formed of uncoated acrylic. As can be seenfrom Table 1, the use of a mixture containing more of the lessaggressive component (SR 150) than the aggressive component (SR 340)resulted in less lens damage. Lens damage means the lens was deemed tobe not optically acceptable. One type of observed lens damage is when aportion of the mold is stuck on the lens after de-molding.

TABLE 1 Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 SR 340 010 15 20 30 50 100 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 0.35Lens Damage No No No No Yes Yes Yes (minor) (Light) (Heavy)

Example 2

The molds for Example 2 were formed of uncoated acrylic. As can be seenfrom Table 2, the use of a mixture containing more of the lessaggressive component (SR 150) than the aggressive component (CN 131) hadless lens damage.

TABLE 2 Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 CN 131 010 15 20 30 50 100 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 0.35Lens Damage No No No No Yes Yes Yes (Minor) (Light) (Heavy)

Example 3

The molds for Example 3 were formed of uncoated acrylic. As can be seenfrom Table 3, the use of a mixture containing more of the lessaggressive component (SR 150) than the aggressive component (SR 203) hadless lens damage.

TABLE 3 Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 SR 203 010 15 20 30 50 100 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 0.35Lens Damage No No No No Yes Yes Yes (Minor) (Minor) (Heavy)

Examples 4 to 6

Examples 4 to 6 below show the effect of temperature on curing variouslens materials. As can be seen, increasing the cure temperature to 50°C. can result in a damaged lens, and sometimes to a milky lens.

Example 4

The molds for Example 4 were formed of uncoated acrylic. As can be seenfrom Table 4, the higher temperatures at which the lenses were castresulted in more lens and/or mold damage and haze formation.

TABLE 4 Formulation 1 2 3 4 5 6 Temperature Room 50° C. Room 50° C. Room50° C. temp. temp. temp. SR 150 100 100 80 80 50 50 SR 340 0 0 20 20 5050 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens Damage/ No/NoNo/No No/No Yes/Yes No/No Yes/Yes Haze

Example 5

The molds for Example 5 were formed of uncoated acrylic. As can be seenfrom Table 5, the higher temperatures at which the lenses were castresulted in more lens and/or mold damage and haze formation.

TABLE 5 Formulation 1 2 3 4 5 6 Temperature Room 50° C. Room 50° C. Room50° C. temp. temp. temp. SR 150 100 100 80 80 50 50 CN 131 0 0 20 20 5050 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens Damage/ No/NoNo/No No/No Yes/No Yes/No Yes/Yes Haze

Example 6

The molds for Example 6 were formed of uncoated acrylic. As can be seenfrom Table 6, the higher temperatures at which the lenses were castresulted in more lens and/or mold damage and haze formation.

TABLE 6 Formulation 1 2 3 4 5 6 Temperature Room 50° C. Room 50° C. Room50° C. temp. temp. temp. SR 150 100 100 80 80 50 50 SR 203 0 0 20 20 5050 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens Damage/ No/NoNo/No No/No Yes/Yes No/No Yes/Yes Haze

Example 7

The molds for Example 7 were formed of acrylic. Example 7 shows lensdamage comparing coated molds and uncoated molds. Table 7 exhibits thepotential advantages of coating the molds prior to filling withformulation and subsequent curing.

TABLE 7 Formulation 1 1 2 2 Mold Coated No Yes No Yes Temperature RoomTemp. Room Temp. 50° C. 50° C. SR 150 0 0 80 80 SR 340 100 100 20 20Photo-initiator 0.35 0.35 0.35 0.35 Damage/Haze Yes/No No/No Yes/YesNo/No

Examples 8 to 10

Examples 8 to 10 provide mold-formulation interaction data for moldsmade from a variety of polymers. The following information can beascertained from the examples: First, different mold materials behavedifferently. In addition, coating the molds suitably can help preventmold and lens formulation interaction, and minimizing the time the lensformulations are in contact with the molds prior to cure is anadvantage. The lower the mold and lens formulation temperature is, priorto and during cure, the less likely mold-formulation interaction is tooccur. Finally, under suitable conditions it is possible to cure andsuccessfully separate molds and formulations without pre-coating themolds. [For tables 8, 9, and 10, only the test material is listed. Theremainder of the formulation in these examples consists of SR-150 andphotoinitiator(s). In Examples 8–10, “No” means there was no lens damageas defined in Example 1, “Yes” means lens damage was observed.]

Example 8

Example 8 shows temperature and time as factors in lens manufacture,using acrylic molds.

TABLE 8 Material Ebecryl 1039 SR 340 CN 131 Ebecryl 810 % Material Temp.Time Coated Uncoated Coated Uncoated Coated Uncoated Coated Uncoated 0RT 10 Min. No No No No No No No No 30 Min. No No No No No No No No 60Min. No No No No No No No No 10 RT 10 Min. No No No No No No No No 30Min. No No No No No No No No 60 Min. No No No No No No No No 30 RT 10Min. No No No No No No No No 30 Min. No No No No No No No Yes 60 Min. NoNo No No No No No Yes 50 RT 10 Min. No No No No No Yes No Yes 30 Min. NoNo No No No Yes No Yes 60 Min. No No No No No Yes No Yes 100 RT 10 Min.No Yes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min.No Yes No Yes No Yes No Yes 0 50° C. 10 Min. No No No No No No No No 30Min. No No No No No No No No 60 Min. No No No No No No No No 10 50° C.10 Min. No Yes No Yes No No No No 30 Min. No Yes No Yes No No No No 60Min. No Yes No Yes No No No No 30 50° C. 10 Min. No Yes No Yes No Yes NoYes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes NoYes 50 50° C. 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No YesNo Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 100 50° C. 10 Min. NoYes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. NoYes No Yes No Yes No Yes

Example 9

Example 9 shows temperature and time as factors in lens manufacture,using polystyrene molds.

TABLE 9 Material Ebecryl 1039 SR 340 CN 131 Ebecryl 810 % Material Temp.Time Coated Uncoated Coated Uncoated Coated Uncoated Coated Uncoated 0RT 10 Min. No No No No No No No No 30 Min. No Yes No Yes No Yes No Yes60 Min. No Yes No Yes No Yes No Yes 10 RT 10 Min. No No No Yes No Yes NoNo 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes NoYes 30 RT 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No Yes NoYes No Yes 60 Min. No Yes No Yes No Yes No Yes 50 RT 10 Min. No Yes NoYes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes NoYes No Yes No Yes 100 RT 10 Min. Yes Yes Yes Yes No Yes No Yes 30 Min.Yes Yes Yes Yes No Yes No Yes 60 Min. Yes Yes Yes Yes No Yes No Yes 050° C. 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No Yes No YesNo Yes 60 Min. No Yes No Yes No Yes No Yes 10 50° C. 10 Min. No Yes NoYes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes NoYes No Yes No Yes 30 50° C. 10 Min. No Yes No Yes No Yes No Yes 30 Min.No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 50 50°C. 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes NoYes 60 Min. No Yes No Yes No Yes No Yes 100 50° C. 10 Min. Yes Yes YesYes No Yes No Yes 30 Min. Yes Yes Yes Yes No Yes No Yes 60 Min. Yes YesYes Yes No Yes No Yes

Example 10

Example 10 shows temperature and time as factors in lens manufacture,using polycarbonate molds.

TABLE 10 Material Ebecryl 1039 SR 340 SR 203 SR 506 % Material Temp.Time Coated Uncoated Coated Uncoated Coated Uncoated Coated Uncoated 0RT 10 Min. No No No No No No No No 30 Min. No No No No No No No No 60Min. No No No No No No No No 10 RT 10 Min. No No No No No No No No 30Min. No No No No No No No No 60 Min. No No No No No No No No 30 RT 10Min. No No No No No Yes No No 30 Min. No No No No No Yes No No 60 Min.No Yes No Yes No Yes No Yes 100 RT 10 Min. No Yes No Yes No Yes No Yes30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No*Yes* 0 50° C. 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No YesNo Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 10 50° C. 10 Min. NoYes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. NoYes No Yes No Yes No Yes 30 50° C. 10 Min. No Yes No Yes No Yes No Yes30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes100 50° C. 10 Min. No* Yes* No Yes No Yes No Yes 30 Min. No* Yes* No YesNo Yes No* Yes* 60 Min. No* Yes* No Yes No Yes No* Yes* *During the holdperiod attack on the uncoated side caused it to leak. The coated sideexhibited no evidence of attack.

Although the present invention has been described with reference tospecific details of certain embodiments thereof, it is not intended thatsuch details should be regarded as limitations upon the scope of theinvention except as and to the extent that they are included in theaccompanying claims.

1. A casting device, comprising: a. a ring having an interior periphery;b. a plurality of front molds, each front mold formed of a plastic andhaving a lens-forming surface, and the front molds providing an edgecircumscribing the lens-forming surface that is sized to becomplementarily received within a portion of the interior periphery ofthe ring, and a base having dimensions greater than the interiorperiphery; and c. a rear mold formed of a plastic and having alens-forming surface, the rear mold configured to be paired with each ofthe plurality of front molds, a rim circumscribing the lens-formingsurface that is sized to be complementarily received within a portion ofthe interior periphery of the ling, and a flange having dimensionsgreater than the interior periphery; wherein when the edge of each ofthe front molds and the rim of the rear mold are configured to bereceived by the ring, the lens-forming surfaces of the front and rearmolds and the ring form a mold cavity which has dimensions of a desiredlens formable therein; and wherein the plurality of front molds areconfigured to form lenses of different effective diameters.
 2. Thecasting device of claim 1, wherein the ring comprises plastic.
 3. Thecasting device of claim 1, wherein the ring further defines a feedopening and a vent opening therethrough in fluid communication with themold cavity.
 4. The casting device of claim 3, wherein, when the frontand rear molds are disposed upright, the vent opening is positioned atsubstantially the top center.
 5. The casting device of claim 3, whereinthe mold cavity is substantially is substantially circular in plan viewand the feed opening is offset from the vent opening betweenapproximately fifteen to ninety degrees.
 6. The casting device of claim2, wherein the ring has opposed ends, wherein the base of the front moldhas a contacting surface that is substantially planar, and wherein thecontacting surface and one end of the ring abut when the mold cavity isformed.
 7. The casting device of claim 6, wherein the lens-formingsurface of the front mold is concave and defines a nadir, wherein thenadir tangentially intersects a plane defined by the contacting surfaceof the base.
 8. The casting device of claim 7, wherein the flange of therear mold has an engaging surface that is substantially planar andwherein the engaging surface and one end of the ring abut when the moldcavity is formed.
 9. The casting device of claim 8, wherein thelens-forming surface of the rear mold has an apex so that a planetangential to the apex is substantially parallel to and spaced apartfrom a plane defined by the engaging surface, the separation between theplane tangential to the apex and the plane defined by the engagingsurface is the back mold apex height.
 10. The casting device of claim 9,wherein the ends of the ring are spaced apart by a ring height, the ringheight being the sum of the back mold apex height and a desired centerthickness for the mold cavity.
 11. The casting device of claim 8,wherein the lens-forming surface of the front mold further comprises aplurality of protrusions each located adjacent the edge, the protrusionshaving a height corresponding to a desired edge thickness for the moldcavity.
 12. The casting device of claim 1, wherein the front mold isrotatable relative to the rear mold so that the two molds are at one ofa plurality of selected rotational orientations relative to each otherso as to alter characteristics of the mold cavity when the lens-formingsurfaces of the respective front and rear molds have asymmetriccurvature.